The present invention relates to a cooling structure for a gas turbine. More particularly, this invention relates to a cooling structure for a gas turbine improved in the film cooling structure for high temperature members such as platform of turbine moving blade.
To enhance the heat efficiency of gas turbine used in generator or the like, it is effective to raise the temperature of the operating high temperature gas at the turbine inlet, but the turbine inlet temperature cannot be merely raised because the heat resisting performance of turbine materials exposed to high temperature gas (hereinafter called high temperature members), including the turbine moving blades and turbine stationary blades, is specified by the physical properties of the materials.
Accordingly, it has been attempted to enhance the heat efficiency within the range of heat resisting performance of high temperature members by raising the turbine inlet temperature while cooling the turbine high temperature members by a cooling medium such as cooling air.
Cooling methods of high temperature members include the convection heat transfer type of passing cooling air into the high temperature members, and keeping the surface temperature of high temperature members lower than the temperature of high temperature gas by heat transfer from high temperature members to cooling air, the protective film type of forming a compressed air film of low temperature on the surface of high temperature members, and suppressing heat transfer from the high temperature gas to the high temperature member surface, and the cooling type combining these two types.
The convection heat transfer type includes convection cooling and blow (collision jet) cooling, and the protective film type includes film cooling and exudation cooling, and among them, in particular, the exudation cooling is most effective for cooling the high temperature members. However, it is difficult to process the porous material used in exudation cooling, and uniform exudation is not expected when pressure distribution is not uniform, and therefore among the practical methods, the cooling structure by film cooling is most effective for cooling high temperature members, and in the gas turbine of high heat efficiency, the cooling structure combining the convection cooling and film cooling is widely employed.
In the cooling structure by film cooling, meanwhile, it is required to form diffusion holes for blowing out cooling air, by discharge processing or the like, from the inner side of the high temperature members or the back side of the surface exposed to high temperature gas, to the surface exposed to the high temperature gas. Hitherto, the diffusion holes were formed so as to open toward the direction of the primary flow of high temperature gas flowing along the high temperature members.
However, the flow of high temperature gas is disturbed to form complicated secondary flow advancing in a direction different from the primary flow due to various factors, such as sealing air leaking between the platform of turbine moving blade and inner shroud of the turbine stationary blade, air leaking between the split ring which is the peripheral wall disposed opposite to the tip side (the leading end in the radial direction) of the turbine moving blade and the outer shroud of the turbine stationary blade, and a pressure difference after collision against the passage wall such as blade, split ring, platform, and shroud.
Accordingly, the cooling air blown out along the primary flow direction is scattered by the secondary flow, and the cooling effect on the high temperature members cannot be exhibited sufficiently.
It is an object of the present invention to provide a cooling structure for a gas turbine enhanced in the cooling effect of film cooling as compared to the conventional art.
The cooling structure for a gas turbine according to one aspect of the present invention is a cooling structure for a gas turbine forming multiple diffusion holes in high temperature members of gas turbine for blowing cooling medium to outer surface of high temperature members of gas turbine for film cooling of the high temperature members, in which the diffusion holes are formed so as to open in a direction nearly coinciding with the secondary flow direction of high temperature gas flowing on the outer surface of the high temperature members.
According to the above-mentioned cooling structure, since the cooling medium blown out from the diffusion holes of the high temperature members is blown out in a direction nearly coinciding with the secondary flow direction of the high temperature gas flowing on the outer surface of the high temperature members, the blown-out cooling medium is not disturbed by the secondary flow of the high temperature gas, and an air film as protective layer is formed on the surface of the high temperature members, so that a desired cooling effect may be given to the high temperature members.
High temperature members of gas turbine include, for example, turbine moving blade, turbine stationary blade, platform of turbine moving blade, inner and outer shrouds of turbine stationary blade, and turbine combustor.
As the cooling medium, cooling air may be used, and the cooling air may be obtained, for example, by extracting part of the air supplied in the compressor of the gas turbine, and cooling the extracted compressed air by a cooler.
The secondary flow is caused by leak of sealing air, or due to pressure difference in the passage after high temperature gas collides against the blade, and the flow direction may be determined by flow analysis or experiment using actual equipment. The direction nearly coinciding with the secondary flow direction is in a range of about xc2x120 degrees of the secondary flow direction, preferably in a rage of xc2x110 degrees, and most preferably in a range of xc2x15 degrees.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.